Expose native, desktop and mobile gesture detection defaults

ui/events/gesture_detection/scale_gesture_detector.cc

Index: ui/events/gesture_detection/scale_gesture_detector.cc
diff --git a/ui/events/gesture_detection/scale_gesture_detector.cc b/ui/events/gesture_detection/scale_gesture_detector.cc
index 7afe91fd3af28e90672f82002d1523495d98ce27..676d6a428183fc79730e12a2616e7a9f9fd5a4a6 100644
--- a/ui/events/gesture_detection/scale_gesture_detector.cc
+++ b/ui/events/gesture_detection/scale_gesture_detector.cc
@@ -30,7 +30,8 @@ const float kScaleFactor = .5f;
 }  // namespace
 
 // Note: These constants were taken directly from the default (unscaled)
-// versions found in Android's ViewConfiguration.
+// versions found in Android's ViewConfiguration. Do not change these default
+// values without explicitly consulting an OWNER.
 ScaleGestureDetector::Config::Config()
     : span_slop(16),
       min_scaling_touch_major(48),